Structures and processes incorporating permeable membranes for the support of animallife during unfavorable conditions



Feb. 20, 1968 W. L. ROBB 3,369,343

STRUCTURES AND PROCESSES INCORPORATING PERMEABLE MEMBRANES FOR THESUPPORT OF ANIMAL LIFE DURING UNFAVORABLE CONDITIONS 1965 4 Sheets-Sheet1 Original Filed June 24,

In ventor': Wa/ter-LJQob by N12? Attorney.

Feb. 20, 1968 w. L. ROBB 3,359,343

STRUCTURES AND PROCESSES INCORPORATING PERMEABLE MEMBRANES FOR THESUPPORT OF ANIMAL LIFE DURING UNFAVORABIJE CONDITIONS Original FiledJune 24, 1965 4 Sheets-Sheet a:

F ig. 3.

Schematic Diagram of Powered System for Extracting Air from Sea Water'Largefxcess of 36 Air Saturated Sea Water 33 u n .L/

f E vacuuted Qnamber Silicone 'fiubber submarm" 37 antral-"e,

F ii! compressor Extracted 34 S Air35% 0,

Cooling 0017s l 38 Liquid Desa/inated H 0- Fig. .4.

Schematic Diagram of Submarine Air Supply Crew Quarters AirSupp/y from NLiters/min. M Liters/min. fxhaust Sea Waterfltractar atm Pressure A y mmWater 0 6.3.2 4 N 20% 02 0.3% 60 I [5 0 4 Liters O /mm. consumed 3.2Liters CO /min. produced 7 C0 and H 0 Removal System 0 Balance 0.35 xiV= 4 Liters/min-i 020x41 Ag Balance 0.632xiV= 0.79xM

-= Zi/Liters/min. of 35% a 7yg 7f0r;

Walter L. Robb,

His Attorney W. L. ROBB Feb. 20, 1968 STRUCTURES AND PROCESSESINCORPORATING PERMEABLE MEMBRANES FOR THE SUPPORT OF ANIMAL LIFE DURINGUNFAVORABLE CONDITIONS Original Filed June 24, 1965 4 SheetsSheet lfisAttor n gay.

Q leb. 20, 1968 w. L. ROBB 3,369,343

STRUCTURES AND PROCESSES INCORPORATING PERMEABLE MEMBRANES FOR THESUPPORT OF ANIMAL LIFE 7 DURING UNFAVORABLE CONDITIONS Original FiledJune 24, 1965 4 Sheets-$heet L Inventor: /0 T T T T T T Wa/fei Lfiobb,

His Af/omy.

United States Patent 8 Claims. (CI. 55-46) ABSTRACT OF THE DISCLOSUREVarious enclosures, structures and methods for supporting animal lifeprocesses in the low pressure rarified expanse of space, at normalatmospheric pressure during unfavorable environmental conditions andunder Water at significant depths are described. In each instance one ormore of the following are accomplished: (a) the removal of carbondioxide gas from exhaled breath to the ambient, (b) the replenishment ofoxygen gas to exhaled breath from the ambient and (c) the simultaneousremoval of both oxygen and nitrogen from surrounding water. In each casegas transfer to and/ or from the ambient is via a thin permeable,non-porous wall, made of a material such as silicone, rubber, properlysupported against rupture in the event of the application of a pressuredifferential to the wall. A method for preparing sound thin membraneshaving a thickness of less than about 2 mils is also described.

making available dissolved oxygen from the water (b) to survivalshelters and respirators for the protection of personnel in the presenceof atmospheric contamination.

Silicone rubber membranes have been found to be particularly applicableto use in this invention and the method for making thin, substantiallydefect-free (e.g., nonporous or hole-free), organopolysiloxane rubberyfilms is described herein. This process comprises l) bringing intointimate contacting relationship at least two films of anorganopolysiloxane convertible to the cured, solid, elastic state oversubstantially the entire contact surfaces thereof, (2) applying pressureto the contacting films to insure the removal of substantially all airfrom between the films, (3) stretching the films while in suchcontacting relationship whereby the thickness of each film is reduced toless than its original thickness and (4) converting the films of reducedthickness to the cured, solid, elastic state while still in saidcontacting relationship whereby permanent intimate bonding of the filmsurfaces is effected.

Silicone rubber membranes have been found to have an unusual ability toseparate certain gases from mixtures of the latter and other gases.Thus, in Kammermeyer US. Patent 2,966,235, issued Dec. 27, 1960, thereis disclosed a method of separating carbon dioxide from a gas mixturecontaining carbon dioxide and other gases, such as hydrogen, nitrogen,oxygen and helium, by permeation of the gases through a thin, non-poroussilicone rubber membrane; In accordance with this patent, it has beenfound that the thin, non-porous silicone rubber membrane will permit amuch greater flow of carbon dioxide than any of the other gasesmentioned above so that the permeation of carbon dioxide through thismembrane is much higher than that of the other gases in relation totheir relative initial concentrations. Generally, this means ofseparating carbon dioxide, for instance, from air, so as to obtain aresidual air mixture leaner in carbon dioxide (by relative proportion)is carried out by bringing the mixture of gases containing carbondioxide, e.g., the aforesaid air, into contact with one side of a thin,non-porous membrane of silicone rubber, causing a portion of the mixtureto permeate through the membrane (under the driving force of adifference in total pressure) said permeated portion of the mixturebeing enriched in carbon dioxide, while the remaining air which did notpermeate the membrane is depleted in carbon dioxide.

When one employs air of normal composition (CO about 05%, O -20.95%,Al%, N -78%) as the mixture of gases being brought in contact with thesilicone rubber membrane, it will be found that when a lower totalpressure exists on the other side of the membrane the mixture of gasespermeating the membrane, in addition to being enriched in carbondioxide, is also enriched to a considerable extent in its oxygen content(since silicone rubber is more permeable to oxygen than to nitrogen),while the gases which did not permeate the membrane are proportionatelyincreased predominantly in their nitrogen content.

The amount of gas that can permeate through a membrane of a given areain a given time is, however, dependent upon its thickness, in additionto other factors such as the pressure drop across the membrane. It is,therefore, seen that optimum results can be obtained when the thinnestpossible membrane, which will withstand the pressure drop across themembrane, is used.

At the present time, silicone rubber compositions can be calendered togive relatively thin films of thicknesses ranging from about 2 to 10mils in thickness. Silicone rubber membranes of such thicknesses areordinarily capable of effecting some separation of gases. However, itwould be highly desirable to use thinner films of the silicone rubbermembrane so that a smaller total area of membrane would be required toprocess a given amount of gas mixture.

When attempts are made to reduce the thickness of the film below 2 to 4mils by the usual techniques heretofore known for making thin films, forexample, calendering, extruding, casting from solution, etc., severaldifficulties are encountered. Thus, it has been found that in makingmembranes of even less than about 5 mils in thickness by the usualtechniques, non-uniformity in thickness and pinholes occur, both ofwhich aspects are detrimental to the utility of the film as a gaspermeable membrane. In addition, tearing often occurs as the thicknessof the membrane is reduced by the usual techniques because of the lackof adequate strength of the silicone rubber membrane so reduced inthickness to Withstand the processing strains encountered with suchtechniques.

Silicone rubber membranes of thicknesses as low as 0.1 mil can beproduced by bringing into intimate contacting relationship so as toexclude all air from between the contacting surfaces at least twoincompletely cured films of silicone rubber, each capable of beingconverted to the completely cured, solid, elastic state; stretching thefilms while in intimate, air-free contacting relationship so that thethickness of each film is reduced to less than the original thickness;and finally, converting the silicone rubber film (while so stretched) tothe cured, solid, elastic state by usual means, for example, by heat(using curing agents for the purpose), or by irradiation with highenergy radiation, as for instance, high energy electrons.

The term silicone rubber is intended to include both 'filled andunfilled organopolysiloxanes which are convertible to the cured, solid,elastic state by any of the means available in the art, for instance, byheating at elevated temperatures in the presence of cure acceleratorssuch as organic peroxides, etc., by irradiation with high energyelectrons as is more particularly disclosed in U.S. Patent 2,763,609,issued Sept. 18, 1956, etc.

The term air as employed herein is intended to in clude variations inpercentages of the components from the normal mixture of gasesencountered in dry atmospheric air at sea level.

The term wall as applied herein to describe part of an enclosurestructure is intended to include any portion of the structurefunctioning as a separating barrier, e.g. side wall or ceiling.

The convertible organopolysiloxane or silicone rubbers such as may beused in the practice of this invention may be in the form of highlyviscous masses or gummy elastic solids, depending upon the state ofcondensation, the condensing agent employed, the startingorganopolysiloxane used to make the convertible organopolysiloxane, etc.More details of the preparation of suitable starting materials arepresented in the aforementioned application S.N. 466,698.

It is, therefore, the prime object of this invention to provide novelstructures for supporting and rendering safe animal life processes inother than normal environrnents.

Other objects of the invention will become more apparent from thediscussion below.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawings wherein:

FIG. 1 is a sechematic illustration of a portable permeable film packfor the protection of personnel, when present in atmospherescontaminated with radioactive airborne particles, germs and/ or chemicalwarface agents;

FIG. 2 is a cutaway view of a survival shelter for use during periods ofatmospheric contamination by radioactive air-borne particles, germs and/or chemical warfare agents:

FIG. 3 is a schematic diagram of a system for extracting oxygen-rich airfrom sea water;

FIG. 4 is a flow diagram illustrating the passage of gases to and fromthe crew quarters of a submarine using the system shown in FIG. 3;

FIG. 5 schematically illustrates apparatus for supplying breathing airfor a miniature submarine by extracting dissolved oxygen from the watersurrounding the submarine while submerged;

FIG. 6 is a more detailed three-dimensional view of the manner ofmounting the permeable film for use in such arrangements as areillustrated in FIGS. 1, 3 and 5;

FIG. 7 schematically represents a membrane cell construction forremoving CO H and human odor from a vehicle, such as a space capsule,wherein the pressure outside the vehicle is lower than the pressure inthe vehicle; and

FIGS. 8 to 12 show one method of producing unbacked thin films for usein this invention.

As shown in FIGS. 1-7, permselective membranes of increasedefiectiveness find particular application in the securing for humans(and, if desired, for animals) of safe oxygenating environments underadverse conditions. Of the apparatuses shown, permeation is efiected bythe application (or presence) of a difference in total pressure on theopposite sides of the permeable membrane in the structures in FIGS. 3and 7, while in the structures in FIGS. 1, 2 and the driving force toefiect permeation is the difference in partial pressures of the gases tobe 4 exchanged (CO to be removed from the breathing air and O to beadded thereto).

Thus, in FIG. 1 is shown a portable air regenerator apparatus 10 usingpermselective membranes to provide breathing air for an individualpresent in surroundings rendered hostile by chemical toxicity, germsand/ or radioactivity. Preferably the apparatus 10 comprises an airtightmask 11 to which is connected a box 12 containing several square yardsof thin silicone rubber film 13 having a uniform thickness preferably inthe range of from 0.1 to 1.0 mil. The range may be extended to employfilms of 2.0 mils thickness, but the vast area of film that would berequired by using films of greater thickness than 2.0 mils would renderthe device impractical. This film 13 is so arranged in box 12 that thewearers breathing air is contained by film 13 on one surface thereof,while contaminated atmospheric air is presented to the opposite surfaceof film 13. The expired breathing air, which is depleted in 0 andenriched in CO and water vapor, is circulated past the permeable filmvia hose 14 and manifold header 16 by the normal action of theindividuals respiratory muscles resulting in contraction and expansionof the lungs. As this expired air flows by the separate layers of film13 from the header 16, the partial pressure driving force for CO watervapor and 0 between the outside air and the expired air causes CO andWater vapor to permeate to the outside, while 0 permeates inwardly toregenerate the expired air, which is collected at manifold header 17 andreturned to mask 11 via hose 18. The path travelled by the spent air maybe lengthened by the use of baffles 19 extending between each set offilms. Also positive circulation is insured by the use of a one-wayvalve (not shown) in hose 14.

Since permeation is actually a solution process in which the gasesdissolve in the film and then diffuse through the film in the dissolvedstate, the film 13 forms a pore-free barrier to any solid, liquid orgas, which does not chemi' cally dissolve in the silicone rubber.

The driving force required to circulate the expired air past thepermeable film 13 is less than a tenth of an inch of water pressure,that mainly being the driving force required to actuate the light-weightcheck-valve (not shown). This driving force is less than that requiredto pull gas through a dust filter, and this gives little discomfort tothe wearer. Outside air is brought in contact with the permeable film 13by ordinary gaseous diffusion, and by convection of the warmed outsideair up through the channels 20 in pack 12, this air being warmed by theheat carried in a mans breath. As shown more clearly in FIG. 6 outsidefluid channels (such as channels 20) Will alternate with channelsreceiving the expired air.

As an example, approximately 10.5 square yards of one-mil silicone filmmay be carried in pack 12. This would be sufficient to maintain awearers inhaled air at an oxygen content of 16 percent and a carbondioxide content of one percent, assuming he was walking at 2 mph (i.e.400 cc. O /min. consumed). At this oxygen concentration he would beworking at an oxygen partial pressure equivalent to that found at 7000ft. above sea level.

Since the wearer does not have to carry an 0 source or CO absorber, oran adsorber for contaminants, he can use this oxygen regenerating andpurifying system indefinitely without recharging or shutting down in anyway. No recurring charge for chemicals will be necessary, and theinitial cost of the film pack should be of the same order of magnitudeas for present micro-porous filters. The pack is very light in weight,because of the reliable thinner silicone film now developed.

Such an air purifying system would be useful in the followingenvironments:

(1) In manufacturing areas containing plutonium, thori-.

um, or beryllium dust; (2) In bacterial or germ-laden areas;

(3) In dust-filled or pollen-filled areas;

(4) In smoke-filled areas, as long as was not depleted,

(5) In areas contaminated with certain nerve gases.

A similar use of silicone permselective membranes can be made infall-out shelters as shown in FIG. 2. The outside contaminated air bypermeating the silicone rubber membranes will lose the contaminants inthe air and purified air containing a sufiicient concentration of oxygenwill be produced in fall-out shelter 21.

Although much has been printed concerning the requirements of fall-outshelters for securing protection against external radiation, little hasbeen said about the means of providing clean, safe air for theinhabitants of such a shelter. It is generally supposed that a filtercan be used to provide fresh air, but the design of such a filter ismost complex. It must provide protection against radioactive airborneparticles, against germs, and against chemical warfare agents for aslong as several weeks and the energy requirements for pulling airthrough the filter must be low.

Another method proposed is to seal off the shelter from outside air, anduse certain chemicals in the shelter to absorb CO and others to release0 Not only are such chemicals expensive, but they have a maximumcapacity, which depends on the amount thereof stored in the shelter.

As opposed to these latter methods of providing fresh clean air, withthis invention air within the shelter is continuously passed over oneside of each of a plurality of polymer films 22, each of which hasoutside contaminated air in contact with its opposite surface. Oxygenpermeates from the outside air through the film 22 in gas exchanger 23into the shelter 21, and simultaneously CO and water vapor permeate fromthe spent air in the shelter 21 outwardly through the film and into theoutside air. In the case of silicone rubber membranes the permeationrate for water vapor is even greater than for CO and as a result thelimiting factor for the extent of silicone rubber film area required ismet by designing for CO -O exchange. Given a sufiicient area of highlypermeable film 22, an 0 content of 16 to 18 percent and a C0 contentbelow one and one-half percent can be easily maintained in the shelter.Since the film 22 is permeable (and not porous) dust, germ cells, etc.cannot pass through the film. Under these conditions, living could go onindefinitely, with no danger of contaminated air getting into theshelter.

One possible design for this permeator or gas exchanger 23 is shown inFIG. 2. Outside air is circulated by natural convection throughopen-ended alternate channels 24 in the permeator 23, while the insideair is circulated through the other alternate channels 26 by one ofseveral methods. These alternates include (1) natural convection due tothe shelter air being warm, (2) as small hand air blower, or (3) facemask which would use the power of the respiratory muscle to circulatethe air. In the arrangement shown air exhaled in the living space 27passes by convection up through conduit 28 into manifold 29 and throughchannels 26, where the reduction in CO content and increase in 0 contenttakes place. The air so refreshed passes from manifold 31 to livingquarters 27 via return duct 32 by natural convection.

Another of the more important uses to which permselective membranes canbe put is to extract oxygen from water to support life. This particularmeans for obtaining air is especially adaptable for supply of breathingair to submarines (as shown in FIGS. 3-5), which remain under water forindefinite periods of time. The capability of certain films withparticular permeation capabilities to extract air from water dependsupon the fact that the water of most oceans to a depth of about 100meters, is saturated with atmospheric oxygen to from 90 to 105 percentthe saturation value at standard conditions of temperature and pressure.To a certain extent, this process simulates the gills of a fish, exceptthat in this case there is an extra gas phase present between the seawater and the blood stream.

In order to better understand how this gas extraction from water occurs,it is necessary to be cognizant of certain principles controlling thebehavior of permeable films. Contrary to general belief the rate ofpermeation of a gas through a film is proportional to the activitygradient across the film, and is not proportional to the absolutepressure gradient. Activity may be related to pressure by an activitycoefficient, which may be expressed as the ratio of the fugacity to thepressure and this ratio is equal to unity for an ideal gas. This term ismore completely defined in the Textbook of Physical Chemistry-Glasstone(2nd editionVan Nostrand Company, Inc.--l946) on page 301.

In the case wherein a liquid phase is present on one side of the film,the pressure and activity gradients can be greatly different, and it isreally the activity gradient which controls the amount and direction ofgas permeating a membrane. Thus, for a given membrane properly supportedagainst the increased pressure applied thereto by the water, if it beassumed that one side of a film is kept at zero pressure and liquidwater at varying pressures is present on the other side of the same filmas would occur at different depths, the rate at which the water willpermeate through the film will remain substantially the same regardlessof whether the water pressure is at 0 .1, 1, or 10 atmospheres for ineach case the activity gradient is approximately equal to the roomtemperature vapor pressure of water. Further the permeation rate willremain substantially the same, even if Water vapor at but a fewcentimeters of pressure is substituted for the liquid water on the highpressure side of the film. Therefore, for a given pressure on the lowpressure side of a permeable membrane, the only way the actualpermeation rate of water can be increased is to increase the temperature(and hence the saturation vapor pressure and. activity) of the water onthe high pressure side of the film. Similarly, if water is saturatedwith air at one atmosphere pressure, the total activity of the gaseouscomponents in the water will remain essentially one atmosphereregardless of What the absolute pressure of the water may become.

Since sea water is saturated with air to a considerable depth, if, forexample, a silicon rubber film 33 (FIG. 3) is supported so that one sidethereof is exposed to a moving stream of water, while the other sidethereof is con tinuously evacuated by compressor or pump 34, oxygen andnitrogen will be extracted from the water, permeating the membrane tothe evacuated side. The mechanical support for the film 33 is, ofcourse, required to enable film 33 to withstand rupture or collapseunder the pressure of the water, which pressure increases with depth. Bycompressing and then cooling the gas and vapor that has permeated film33 a suitable air supply is provided and also some liquid water. ThisWater is even desalinated, so that this method of air extraction notonly extracts breathing air from sea water but also produces potablewater as well. When the film 33 is of silicone rubber, the extractedair, which will be obtained will be enriched in oxygen, because of thehigher permeability of oxygen through the silicone rubber film and also,because of the higher solubility of oxygen in sea water.

As a specific example, one can consider the case of a submarine with aten-man crew and assume that on the average each man in the submarineconsumes 400 cc.s of oxygen per minute and generates 320 cc:.s of carbondioxide per minute. The carbon dioxide concentration can be reduced inthe crew quarters by any one of a number of methods, as for example,chemical adsorption, or by concentration and rejection. This is shownschematically in FIG. 4 as a flow diagram. The latter method may beeffected by the use of films selectively permeable to carbon dioxide.

To maintain an atmosphere containing about 20 mole percent oxygen in thecrew quarters of the submarine, about 21.1 liters per minute of aircontaining about 35 mole percent oxygen would have to be extracted fromthe sea water to sustain the ten-man crew. Based on the knownpermeability of siiicone rubber films, this capacity would be providedby a permeator, or extractor unit 36 with an operating surface of 26square yards of 0.5 to 1 mil silicone rubber film and with a flow ofwater through such a cell of about 75-100 cubic feet per minute. Withthe low pressure side of film 33 being operated at 1 cm. mercury, onlyabout 300 watts of compressive work would have to be expended for aten-man crew and this work demand can be further reduced by increasingthe operating film area in the extractor unit 36. In addition tosupplying the oxygen required for ten men, extractor 36 would alsoprovide about 75 to 90 pounds of desalinated water per day as a usefulbyproduct.

As the large excess of air-saturated sea water passes the face ofsilicone rubber membrane 33, the vacuum on the other side of thesilicone rubber membrane induced by compressor 34 reduces the pressureso as to promote the ermeation of water and oxygen and nitrogen throughthe membrane 33. As this gas is withdrawn from adjacent the membrane 33it is compressed by compressor 34. Next, the water vapor in the gas isremoved by cooling coils 37 and de-entrainer 38. The resulting airstream is oxygenenriched, containing about 35 percent oxygen. The methodfor maintaining the oxygen and nitrogen balance with 35 percent oxygenfeed to the crew quarters is shown in FIG. 4.

Where minimum power is available, for instance in a miniature submarine,it is possible for the operator to regenerate his own breathing airwithout requiring a compressor to remove and compress the gas permeatingthrough the permselective film. Such an arrangement is shown in FIG. 5.

FIG. 6 shows in some detail the manner in which a film pack 40 useablein the apparatuses of FIGS. 1, 3 and would be constructed. The film pack40 is disposed so that the oxygenabearing fluid at higher pressureenters the open ends of alternate channels 41 via inlet holes 42, flowsover the surfaces of silicone rubber permselective membrane 43 ofoptimum construction and exits from the unit 40 via holes 44. In thecase of the application illustrated in FIG. 1 and as well in FIG. 2 theoxygen-bearing fluid is air, which yields oxygen to the breathing airand picks up CO and water vapor therefrom. The oxygen-bearing fluid iswater in the case of the arrangement proposed in FIG. 3 and this waterserves as the source of oxygen, nitrogen and water. In FIG. 5 thearrangement once again employs water as the oxygen-bearing fluid andserves to yield oxygen and to pick up CO through the silicone film. Theoutput header 46 extends through the plurality of frame supports 47,which define the oxygen-bearing fluid channels 41, and communicates withthe breathing air chambers 48, which alternate with channels 41. In asimilar fashion distribution header 49 extends through the framesupports 47 and communicates with the chambers 48 to supply the expelledair thereto to enable the requisite gas exchange to occur. In the usualconstruction porous packing 51 (eg, leached urethane foam, glass fiberbatting, corrugated cardboard, porous metal) is employed in chambers 48to lend support to films 43 to pre vent their collapse toward eachother. Wherever the permselective films would be subjected to asignificant pressure differential as, for example, with increasing depthin underwater applications (FIGS. 3 and 5), mechanical support for thefilm must be able to support the film and still permit passage of gasestherethrough. Obviously upon movement to significant depths man isunable to expand his lungs against the outside water pressure asrequired to cause oxygenabeaiing gases to enter his lungs and underthese circumstances man must isolate himself, or at least his breathingapparatus from direct contact with the water as, for example, within thehull of a submarine.

It is known that man can live and work in an atmosphere having 16 molepercent oxygen and 1.5 mole percent oarbon dioxide. A man inhaling thisair, would exhale air containing about 12 mole percent oxygen and 5 molepercent carbon dioxide. By exhaling this air and conducting it past afilm exposed to air-satunated Water, the activity gradient of the oxygenbetween the oxygenbearing fluid and the gas phase would cause oxygen topermeate through the film into the depleted exhaled air. At the sametime, carbon dioxide would permeate through the film in the oppositedirection, and in this manner the air would be regenerated to thetolerable conditions of 16 percent oxygen and 1.5 percent carbondioxide. However, one condition that is necessary for this gas exchangeto occur in the submarine 52 (FIG. 5) is that suflicient water must movethrough film pack 40 (as shown by the arrows) to supply the requiredoxygen. It is estimated that :a water rate of about 14 cubic feet perminute passing through the film pack 40 over the membranes 43 issufficient. Such a water rate can be obtained either by moving submarine52 through the water at the proper minimum rate of speed or by pumpingthis much water through film pack 40 when the submarine is at rest. Inthe arrangement shown hose 53 connected between face mask 54 anddistribution header 49 is provided with a one-way valve (not shown) andconducts spent breath to film pack 46 for gas exchange with sea. waterpassing therethrough. The regenerated air is returned to face mask 54-via evacuation header 46 and hose 56.

Another serious problem involving the provision of a livealbleenvironment for man (or other animal life) occurs in a space vehicle. Insolving the problem of providing breathing air for capsule inhabitantsthe weight of the system employed is of utmost concern. For shortflights a supply of oxygen can be carried along in the form of liquidoxygen or as pressurized oxygen gas, however, this solution stillrequires provision for the removal of CO water vapor and noxious bodyodors from the vehicle. The means employed so far for effecting suchremoval has been to employ various filters, absorbers and coolingdevices. Although the removal of CO water vapor and noxious body odorscan be effectively accomplished thereby, these solutions to the problemimpose a weight penalty burden that can be substantially reduced byutilizing a permeation system as disclosed herein.

The device shown in FIG. 7 is an illustration of the manner in whichsuch a permeation system may be constructed and employed. The cell 60 isconstructed with the system of alternately arranged channels much as isshown in the film pack 40. However, in this instance the object is topass CO water vapor and noxious odors out of the vehicle into space. Asshown, cell 60 forms part of the external wall 61 of the space vehicle.The air in the space vehicle is conducted into: manifold 62 from whichlit passes into alternate channels 63 to be passed over the surfaces ofmembranes 64. The pressure differential between channels 63 and spaceprovides the driving force for the permeation of CO water vapor and thenoxious gases through the membranes 64 to space via holes 66. In orderto protect membranes 64 against rupture due to this pressuredifferential, porous support means 65 is provided in the chambers shownvented to space through holes 66. The breathing air of reduced impuritycontent then passes to manifold 67 for recirculation into the interiorof the space vehicle. A certain amount of oxygen is also lost to spacethrough the permeable membranes and the replenishing of the gas contentof the space vehicle is accomplished by adding oxygen, as from tank 68,to the air leaving manifold 67, as shown. In Table I, data on siliconerubber as a membrane material are provided. The rates for NH H 8 and thehydrocarbons are indicative of the effectiveness with which body odorswill permeate the membrane.

sec, sq. cm., 0111. Hg

Pyridine By the use of this construction it is proposed to reduce theWeight of the apparatus that must be delegated to the task of removingnoxious gases from the space vehicle. Studies indicate that the size ofthe regenerating permeable membrane cell 60 need not exceed one cubicfoot and could be as small as 0.1 cubic foot.

A preferred method for the preparation of silicone rubber membranesparticularly applicable to use in the novel structures of this inventionis described in connection with FIGS. 8 to 12. Therein is disclosed thefilled silicone rubber film 71 containing a cure accelerator with abacking 72 therefor unwinding from roll 73 with the backing (such ascellulose acetate) being Wound back on roll 73'. The silicone rubberfilm will have been obtained by previous calendering or other suchsuitable means and by giving the silicone film a partial cure by heatingas indicated previously. Any pinholes present in the calendered film maybe patched as described previously with the same material from which thefilm itself is made. These patches 74 are readily adherent to the basefilm in the uncured or incompletely cured state so that a bond ofsufiicient strength is achieved merely by bringing the patch intointimate contact with the film.

FIG. 9 shows a cutaway view of the two films 71 and 71' superposed oneach other prior to establishing contacting relationship; the lack ofcoincidence of the holes in the'films is shown in this view.

Thereafter, as shown in FIG. 10, the dual films 71 and 71' are stretchedfrom about 25 to 500 percent (in one or both directions) and in thisstretched condition are clamped together by means of a frame 75 held inplace by screws 76. This frame and film are held by clamps 77 (only onebeing shown) over the evacuating apparatus 78 as shown in FIG. 11whereby the two films 71, 71', supported on porous screen 79, are forcedinto intimate contact over their entire contact area by the removal ofair from between the films by the application of a vacuum by theevacuating apparatus beneath the films. This application of a pressuregradient to the films effects the elimination of air from between thefilms by permeation. The consolidated film 80 in the stretched, clampedstate is then cured as shown in FIG. 12 by any of the means recitedpreviously, for instance by heating at temperatures from about 150 to250 C. for times ranging from about 2 minutes to 2 hours or more toyield a cured, stretched, consolidated thin film, which then can be usedas a permselective membrane of increased effectiveness, because of itscombined qualities of extra thinness and freedom from perforations.

Preferably at least the final stretching of films 71, 71' is noteffected until the films have been brought into such intimate contact asto eliminate air from between the films either by permeation through onefilm (by the application of a high pressure gradient as in FIG. 11) orby permeation through both films (by the inwardly direction of pressureon both outer faces of films 71, 71' by means of porous metal plates orstructural means with very fine perforations therethrough).

Whereas, if the stretched composite film 80 were released without firstcuring the silicone rubber, the material would revert to its earlierarea, it has been found that the stretched film, when cured, does notshrink or at most shrinks only a small amount upon removal of therestraining force as the stress of stretching is relaxed by the curingstep.

In order that those skilled in the art may better understand how thisinvention may be practiced, the following examples are given by way ofillustration and not by way of limitation. All parts are by weight.

Example 1 An organopolysiloxane material capable of later conversion tothe cured, solid, elastic state was prepared by heating at a temperaturebetween 155 C. with agitation over a period of about 4 hours, 100 partsof octamethylcyclotetrasiloxane in the presence of 0.001 part ofpotassium hydroxide. The resulting polydimethyh siloxane was a highlyviscous, benzene-soluble mass of only slight flow, and had a ratio ofapproximately 2 methyl groups per silicon atom and a viscosity of about6 million centistokes. A mixture of about 100 parts of theabove-described polydimethylsiloxane and 43 parts of fume silica wasmilled on a rubber mill and to the resulting filler-polymer mixture wasadded 1.5 parts of benzoyl peroxide. This mixture of ingredients willhereinafter be referred to as convertible methylpolysiloxane.

Example 2 The above convertible methylpolysiloxane was calendered on atworoll calende-ring mill with a backing of cellulose acetate until asilicone rubber film about 2.543 mils was obtained. Since this siliconerubber film was found to have several pinholes upon visual observations,the pinholes were covered with small pieces of the same calendering film(free of the backing), so that a close bond was effected between thepatch and the base film. This calendered silicone rubber film, which hadbeen given a heat treatment (to effect a light cure) for 30 seconds atC. during the calendering operation, was then separated from thecellulose acetate support film, and two equal areas (9" x 9") of thissilicone rubber film were superposed on each other and stretched incontacting relationship over a frame (see the accompanying FIGS. 11 and12), so that the area of the film was increased to a size approximately500 percent greater than the original composite film (9" x 9"). The twofilms were pressed against each other using air pressure to create apressure differential to force the two component films into intimatecontact. While in the stretched condition in contact with each other,the composite film was then subjected to additional heating for one hourat C. to effect complete cure of the films and bonding of the individualinternal surfaces of the component films to each other. Thereafter, thisunified bonded composite film about 1 mil thick was placed over a formfor use as a permselective membrane. When films of this thickness wereused as gas separating membranes, it was found that the gases removedfrom the opposite sides of the membrane were reatly enriched in oxygenon the one hand and carbon dioxide on the other hand as reported in theaforesaid Kammermeyer patent, but at a rate of gas permeation throughthe membrane considerably in excess of the rates achieved in the past.Also, it was found when such thin films were used for the purposesdescribed in my copending patent application Ser. No. 247,904 (filedDec. 28, 1962 and assigned to the assignee of this invention) gases suchas Xenon and krypton could more readily be removed from mixtures of thelatter gases with oxygen and nitrogen.

Therefore, a number of novel structures have been presented, whosepracticability are considerably enhanced by the development of thehighly improved silicone rubber permeable membrane of substantiallyreduced uniform thickness made by the process described herein andhaving the unique high permeation rates for CO and water 1 1 vaporindicated in Table I. Variations of the process and structuralarrangements proposed herein are contemplated without departing from thescope and intent of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a vehicle for operation in the low pressure rarified expanse ofspace, the vehicle comprising an enclosure for supporting animal lifeprocesses during operation of the vehicle, the improvement comprising:

(a) the wall area of the enclosure being impermeable,

(b) a chamber having permeable non-porous wall area,

(1) said permeable non-porous area being of silicone rubber film locatedoutside the impermeable Wall area of said enclosure and disposed forcontact with the ambient,

(c) first means for conducting high humidity air having a greater carbondioxide concentration and a smaller oxygen concentration therein than ischaracteristic of normal air from within said enclosure to said chamber,

(d) second means for returning air having smaller oxygen concentrationand substantially smaller concentration of carbon dioxide and watervapor than is characteristic of normal air from said chamber to theinterior of said enclosure, and

(e) means disposed Within said enclosure and in fioW communication withsaid second means for adding oxygen to the returning air.

2. In a vehicle enclosure for containing and supporting animal lifeprocesses during transport at significant depths in water containingdissolved air, the improvement comprising:

(a) the wall area of said vehicle enclosure being impermeable and ableto withstand the application of high pressure thereto,

(b) a chamber having permeable non-porou wall area,

(1) said permeable non-porous Wall area being of silicone rubber filmlocated outside the impermeable Wall area of said vehicle enclosure anddisposed for contact with the surrounding Water,

(c) first means for conducting air having a greater carbon dioxideconcentration and a smaller oxygen concentration therein than ischaracteristic of normal air from within said vehicle enclosure to saidchamber,

(d) second means for returning air containing at least about 16 molepercent oxygen and a maximum of 1.5 mole percent carbon dioxide fromsaid chamber to the interior of said vehicle enclosure, and

(e) porous means in contact with one side of said silicone rubber filmfor supporting said silicone rubber film against movement under theapplication of significant pressure by the surrounding Water.

3. In a respirator device for individual use comprising a face mask tobe Worn by the user, a chamber in com munication with said face mask andmeans for removing harmful substance from the air entering said chamber,the improvement comprising:

(a) Wall area of the chamber being constructed of 12 permeable,non-porous material in contact with the atmospheric air, and

(b) means for conducting gases in a circuit to said chamber and back tosaid mask by separate route.

4. The individual air regenerator substantially as recited in claim 3wherein the permeable Wall area is of silicone rubber.

5. The process for extracting an oxygen-containing gas phase from water,which contains air dissolved therein, which comprises:

bringing Water containing dissolved air into direct contact with oneside of a silicone rubber permselective membrane,

simultaneously removing from the opposite side of said membrane oxygenand nitrogen gases and water vapor permeating through said film membersand introducing a difierence in the partial pressure of oxygen andnitrogen gases and Water vapor on said one side as compared to thepartial pressure of oxygen and nitrogen gases and Water vapor on saidopposite side thereby causing the passage of oxygen, nitrogen and watervapor through said membrane to replace oxygen, nitrogen and Water vaporso removed.

6. The process as in claim 8 in which the permselective membrane is apolydimethylsiloxane rubber.

7. The process for extracting oxygen from Water at significant depths,said water containing dissolved air, which process comprises:

passing water across and in direct contact with one surface of apermselective membrane,

mechanically supporting said permselective membrane from movement underthe application of water pressure applied to said one side thereof,

passing an oxygen depleted and carbon dioxide enriched air stream overand in direct contact with the opposite side of said membrane so thatoxygen fro-m the water permeates through said membrane and increases theoxygen content of the air stream, while simultaneously carbon dioxidefrom the air stream permeates through said membrane into the Water.

8. The process as in claim 7 in which the water passed in direct contactwith the permselective membrane is provided at a flow rate of at leastabout 14 cubic feet per minute.

References Cited UNITED STATES PATENTS 307,041 10/1884 Herzog 158693,638 2/1902 Breuer 55158 X 2,223,586 12/1940 Thomas 55158 2,433,74112/1947 Crawford 5516 2,506,656 5/1950 Wallach et al. 5516 2,966,23512/1960 Kammermeyer 55--16 2,970,106 1/1961 Binning et a] 5516 X3,196,871 7/1965 Horrnats et al 55158 X 3,228,394 1/1966 Ayres 128-1423,333,583 8/1967 Bodell 210321 X SAMIH N. ZAHARNA, Primary Examiner.

REUBEN FRIEDMAN, Examiner.

J. ADEE, Assistant Examiner.

